I have to think a bit to organize why and advantages and disadvantages of this, so I thought I'd share.
I define "tokenizing shares" as using a distributed blockchain with universal ability to transact as a way to trade shares.
Advantages of tokenizing shares:
* Universal access to fractional trading, not just inside a single trading platform. (Most likely, anyway.)
* Near zero transaction costs outside the spread. There are trading platforms that offer $0 commissions for regular retail customers, but there's still regulatory fees and these could potentially be skipped. (NOTE: There is likely a larger spread on a distributed ledger than a regular exchange, due to slower transactions. See below.)
* Ability to trade 24h
* Access to purchasers that don't want to or cannot use traditional platforms (e.g, crypto fans, people in developing countries). This may be stopped by "Permissioned ledgers", where there contracts that stop the transfer of stocks into a wallet unless it's on a whitelist.
* Resistance to total failure (due to the distributed nature of the setup)
Changes with good and bad sides:
* Slower trades; expect max speed of milliseconds rather than 1us
* Thus, a loss of the ability to do HFT (High Frequency Trading), which means that we lose the information transmission and market making ability of HFTs, but we also lose their ability to do front-running and decrease their ability to cause flash crashes and similar
* Loss of ability to shut down the trading. This remove an abusable tool of power, but it also lose a tool used to stop bad situation (like flash crashes), which is used to deal with bad market situations (like flash crashes due to trading software bugs), to avoid insider trading when major news is about to hit, and to deal with regulatory concerns.
* All trades are final. In the regular market, trades can be reversed by the courts or banks if done quickly (clearing in the US is in one business day, in Europe it's mostly two business days); in an anonymous, immediate clearing system based on a final distributed ledger, trades can't be reversed. This removes some types of risk, but adds in risks of theft (as we've seen with cryptocurrency) and makes mistakes more difficult to reverse.
Disadvantage if both on a regular exchange and a blockchain:
* The slower trades on the blockchain will lead to latency arbitrage. To avoid losses from price sniping, the blockchain market has to have wider spreads. Market makers will also typically provide limited liquidity in the slower market, to minimize the amount of loss the times they do get sniped.
Disadvantages of stocks on a blockchain in general:
* The distributed nature of the blockchain will allow frontrunning: A retail investor place an order in a market, and a frontrunning company with faster routing setup will then buy the stock elsewhere at a lower price, and re-sell it to the investor at the higher price. If there are distributed validators for transaction order, frontrunners may instead use techniques to bribe the validators (e.g, they may run validators themselves, and have their purchase jump the queue). The net result of both is that instead of negative spread going as profit to the retail investors, it goes to the frontrunners.
* It provides larger liquidity pools for criminals and terrorist organizations to do money laundering; e.g. Russia may be able to move billions around outside sanctions (though there are protocols in place that try to stop this)
Disadvantages for this particular blockchain at this time, for the companies that are resistant to getting on it:
* It is cheap to say no now, and they can't say no later
* There is little time to evaluate
* There is likely some level of legal risk
That's a quick attempt to sort my thoughts - they're not strongly researched for this particular blockchain, though I did a couple of searches to fill in details that I wasn't certain about.